U.S. patent number 4,621,024 [Application Number 06/687,997] was granted by the patent office on 1986-11-04 for metal-coated hollow microspheres.
This patent grant is currently assigned to Paper Applications International, Inc.. Invention is credited to Frederick A. Wright.
United States Patent |
4,621,024 |
Wright |
November 4, 1986 |
Metal-coated hollow microspheres
Abstract
A process for preparing a metal-coated hollow microsphere
comprising the combination of steps of: (a) vigorously admixing a
major quantity of hollow cenospheres/microspheres with a
thermo-setting binder adhesive until the cenospheres are wet-out;
(b) slowly adding metal flakes to the thus wet-out cenospheres of
step (a) until the wet-out cenospheres are fully coated with the
metal flakes; (c) binding the metal flakes to the said wet-out
cenospheres by slowly increasing the temperature of the metal
coated wet-out cenospheres from step (b), the temperature being
raised up to about 350.degree. F.; and (d) the metal-coated
cenospheres of step (c) are intermittently admixed in the absence
of any further heating until dry. The dry product is ready for
packaging.
Inventors: |
Wright; Frederick A.
(Chattanooga, TN) |
Assignee: |
Paper Applications International,
Inc. (Chattanooga, TN)
|
Family
ID: |
24762694 |
Appl.
No.: |
06/687,997 |
Filed: |
December 31, 1984 |
Current U.S.
Class: |
428/404; 427/204;
427/205; 427/214; 427/221; 428/405; 428/406; 428/407 |
Current CPC
Class: |
C09C
1/28 (20130101); C04B 20/12 (20130101); B01J
13/22 (20130101); B01J 13/04 (20130101); C09C
1/405 (20130101); C04B 18/082 (20130101); C01P
2004/51 (20130101); Y02W 30/91 (20150501); C01P
2004/34 (20130101); Y02W 30/92 (20150501); Y10T
428/2996 (20150115); Y10T 428/2998 (20150115); C01P
2004/61 (20130101); Y10T 428/2993 (20150115); C01P
2006/90 (20130101); Y10T 428/2995 (20150115); C01P
2004/84 (20130101) |
Current International
Class: |
C04B
18/04 (20060101); C04B 20/00 (20060101); C04B
18/08 (20060101); C04B 20/12 (20060101); B01J
13/22 (20060101); B01J 13/04 (20060101); B01J
13/20 (20060101); C09C 1/40 (20060101); C09C
1/28 (20060101); B05D 001/36 (); B05D 007/00 ();
B32B 005/16 (); B32B 009/00 () |
Field of
Search: |
;427/205,214,221,204,404
;428/405,406,407 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lusignan; Michael R.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. A process for preparing metal-coated hollow microspheres
comprising the combination of steps of:
(a) vigorously admixing a major quantity of hollow microspheres
with a thermosetting binder adhesive until said microspheres are
wet-out, said hollow microspheres having an average particle size
diameter ranging from about 60 microns to about 180 microns;
(b) slowly adding metal flakes to the thus wet-out microspheres
from step (a) until said wet-out microspheres are coated with said
metal flakes;
(c) applying heat and slowly increasing the temperature of the
metal-coated microspheres from step (b) up to about 350.degree. F.
to thereby cure said binder and bind said metal flakes to said
microspheres; and
(d) intermittently mixing-agitating the metal-coated microspheres
from step (c) in the absence of any further heating until said
metal-coated microspheres are dry.
2. Process according to claim 1, wherein said thermosetting binder
adhesive is composed of a polymerizable organo-silane composition
and a copolymerizable monomer or copolymer.
3. Process according to claim 2, wherein said polymerizable
organo-silane is 3[2(vinyl benzylamino)ethylamino]propyltrimethoxy
silane and said copolymerizable monomer is gamma-butyrolactone.
4. Process according to claim 1, wherein said thermo-setting binder
adhesive is added in amount about 3 to about 4 percent by weight of
the final product.
5. Process according to claim 1, wherein said metal flakes have an
average size of about 6 microns to 10 microns.
6. Process according to claim 1, wherein said hollow microspheres
have an average particle size of about 100 microns to about 150
microns.
7. Process according to claim 1, where in said step (c) the
temperature is raised to about 220.degree. F. to about 240.degree.
F.
8. Process according to claim 1, where in step (a) heat is applied
until a temperature of about 140.degree. F. to about 160.degree. F.
is obtained.
9. Process according to claim 1, wherein said metal flake is
composed of zinc, aluminum, silver, copper, stainless steel,
platinum, gold or a combination thereof.
10. A process for preparing metal-coated hollow microspheres
comprising the combination of steps of:
(a) vigorously admixing a major quantity of hollow microspheres
having an average particle size diameter ranging from about 60
microns to about 180 microns with about 3 to about 6 weight
percent, based on the weight of the final product, of a
thermosetting binder adhesive comprising an organo functional
silane and a copolymerizable monomer, until said microspheres are
wet-out;
(b) slowly adding metal flakes to the thus wet-out microspheres
from step (a) until said wet-out microspheres are coated with said
metal flakes, said metal flakes having an average particle size of
about 6 microns to about 10 microns;
(c) applying heat and slowly increasing the temperature of the
metal-coated microspheres from step (b) up to about 350.degree. F.
to thereby cure said binder and bind said metal flakes to said
microspheres; and
(d) intermittently mixing-agitating the metal-coated microspheres
from step (c) in the absence of any futher heating, until said
metal-coated microspheres are dry.
11. Process according to claim 10, where in step (b) about 15 to
about 30 weight percent metal flakes, relative to said wet-out
microspheres from step (a), are employed.
12. Process according to claim 11, wherein said mircospheres have
an average particle size of about 165 to 170 microns and about 18
to about 22 weight percent metal flakes, relative to said wet-out
microspheres from step (a), are employed.
13. Metal-coated hollow microspheres obtained by:
(a) vigorously admixing a major quantity of hollow microspheres
having an average particle size diameter ranging from about 60
microns to about 180 microns, with about 3 to about 6 weight
percent, based on the weight of the final product, of a
thermosetting binder adhesive, said adhesive comprising an organo
functional silane and a copolymerizable monomer, until said
microspheres are wet-out;
(b) adding metal flakes to the thus wet-out microspheres from step
(a) until said wet-out microspheres are coated with said metal
flakes, said metal flakes having an average particle size of about
2 microns to about 10 microns;
(c) applying heat and slowly increasing the temperature of the
metal-coated microspheres from step (b) until a temperature of up
to about 350.degree. F. is reached to thereby cure said binder and
bind said metal flakes to said microspheres; and
(d) intermittently admixing-agitating the metal-coated microspheres
from step (c) in the absence of further heating until said
metal-coated micrspheres are dry after which said metal-coated
microspheres are recovered as product.
14. Process according to claim 2, which also includes:
pre-heating said microspheres and said binder in said step (a) and
continuing said pre-heating treatment until a temperature of about
140.degree. F. to 160.degree. F. is obtained;
raising the temperature in said step (c) to about 220.degree. F. to
about 240.degree. F.; and
said hollow microspheres having an average particle size diameter
of about 100 microns to about 180 microns and said metal flakes
having an average particle size of about 6 microns to about 10
microns comprising zinc, aluminum, silver, copper, stainless steel,
platinum, gold or a mixture thereof.
15. Process according to claim 14 wherein said thermosetting binder
adhesive is 3 propyltrimethoxy silane and said copolymerizer
monomer is gamma-butyrolactone.
16. The process according to claim 10, wherein:
heat is applied in step (a) until the mixture of said hollow
microspheres and said binder is heated to a temperature of about
140.degree. F. to about 160.degree. F.; and
the temperature in said step (c) is raised to about 220.degree. F.
to about 300.degree. F.,
said hollow microspheres having an average particle size diameter
ranging from about 100 microns to about 180 microns,
said metal flakes being composed of zinc, aluminum, silver, copper,
stainless steel, platinum, gold or a combination thereof.
17. Metal-coated hollow microspheres, comprising non-conductive
hollow microspheres having an average particle size diameter
ranging from about 60 microns to about 180 microns, metal flakes
substantially coating individual said hollow microspheres, said
metal flakes having an interior surface bound to an exterior
surface of a hollow microspheres by a thermosetting binder
adhesive.
18. Metal-coated hollow microspheres according to claim 17 wherein
said hollow microspheres have an average particle size diameter of
about 100 microns to about 180 microns, said metal flakes have an
average particle size of about 6 microns to about 10 microns, and
said thermosetting binder adhesive comprises the reaction product
of an organo functional silane and a copolymerizable monomer.
19. Metal coated hollow microspheres according to claim 18 wherein
said metal flakes are composed of zinc, aluminum, silver, copper,
stainless steel, platinum, gold or a combination thereof.
20. Metal coated hollow microspheres according to claim 17 wherein
said metal coated hollow microspheres have an average particle size
diameter ranging from about 100 microns to about 150 microns.
Description
The present invention relates, broadly, to metal-coated
microspheres. More particularly, the present invention relates to
hollow microspheres having exposed metallic particles bound by a
thermosetting adhesive material to the hollow microspheres.
BACKGROUND OF THE INVENTION
As general background information, the following are mentioned.
U.S. Pat. No. 4,137,367 (1979) discloses phyllosilicate minerals
which are superficially etched with dilute acid to remove an outer
octahedrol layer under specific conditions to preserve structural
integrity. The acid etch is said to expose silanol groups receptive
for subsequent condensation with an organo-silane in a suitable
solvent under mild conditions.
As is also known, cellular glass pellet cores have been bonded to
and coated with fly ash particles. Such pellets are rather large,
on the order of 0.5 to 20 mm. Such materials are described in U.S.
Pat. No. 4,143,202.
Various coupling agents composed of organo-functional silanes plus
an amine silicate and treatments therewith of reinforcing fibers
are also known. Such an amine silicate component has a degree of
polymerization less than 1000. It is said in U.S. Pat. No.
3,649,320 (1976) that the formulations enabled better control over
the spatial arrangement of the coupling agent about the surface of
the reinforcement material.
Efforts to improve the compatability of organic polymers and resins
with pre-heated coal fly ash are disclosed in U.S. Pat. No.
4,336,284 (1982) as partially covering coal fly ash with an
essentially hydrophobic mono-molecular partial coating of a
chemical agent, the thickness being under 100 .ANG..
In the past, efforts to dissipate and control static electrical
build-up necessitated use of carbon powder fillers in composite
materials. These composite materials, laden with carbon, were used
to prevent static electricity build-up in hospitals and, for
example, computer centers. Disadvantageously, however, such
composites exhibited poor physical properties.
SUMMARY OF THE INVENTION
The present invention pertains to a process and a product. The
process provides means for producing metal-coated hollow
microspheres by vigorously admixing hollow microspheres with an
adhesive binder to coat the hollow microspheres, adding metal
flakes to the thus coated hollow, slowly and uniformly heating the
microspheres-binder-metal intermediate product until it reaches a
temperature of up to about 350.degree. F., thereafter
intermittently admixing or tumbling the heated hollow
microsphere-binder-metal intermediate product in the absence of
further heating until the binder is cured, and followed by product
recovery.
An object of the present invention is to provide a simple process
for preparing a metal-coated hollow microsphere.
Yet another object of the present invention is to prepare a unique
metal-coated hollow microsphere wherein there is an exposed metal
surface.
Still another feature of the present invention is to provide
metal-coated hollow microsphere suitable for a wide variety of
end-use applications. Applications include dissipative ingredients,
marine coatings/paints, glassy concrete, EMI shielding, and RFI
shielding.
It is still yet another object of the present invention to provide
a process that obviates the need for acid-pretreatment of hollow
microspheres prior to use.
Other objects, features, and characteristics of the present
invention as well as the method and operation thereof will become
more apparent upon consideration of the following description and
the appended claims all of which form a part of this
specification.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention may be broadly characterized
as composed of the following combination of steps. A selected
quantity of hollow microspheres is vigorously admixed and blended
with an adhesive binder, preferably a thermosetting adhesive
binder, until the hollow microspheres are wet-out, i.e. coated with
the adhesive binder. Next, the desired metal, in the form of
flakes, is slowly added to the wet-out hollow microspheres thereby
providing metal-coated hollow microspheres with exposed metallic
surfaces. Subsequently, the metal flakes are permanently bound to
the hollow microspheres by curing the binder. The curing is
obtained by slowly and uniformly heating the reaction vessel to
raise its temperature up to a maximum of about 350.degree. F.
Following the curing procedure the metal coated hollow microspheres
are intermittently mixed or intermittently tumbled in the absence
of any further heating until the metal-coated hollow microspheres
are dry. The product is then recovered.
The process for preparing a metal-coated hollow microsphere can
advantageously be characterized as comprising the combination of
steps (a) vigorously admixing a major quantity of hollow
microspheres with about 3 to about 6 weight percent (based on the
final product) of a thermosetting binder adhesive until the hollow
microspheres are wet-out; (b) slowly adding metal flakes having an
average size of 6 to 10 microns to the thus wet-out hollow
microspheres of step (a) until the wet-out hollow microspheres are
fully coated with the metal flakes; (c) binding metal flakes to the
wet-out hollow microspheres by slowly applying heat to raise the
temperature of the metal coated-hollow microspheres from step (b),
the temperature is raised up to between about 220.degree. F. to
about 240.degree. F.; and (d) the metal-coated microspheres of step
(c) are intermittently admixed in the absence of any further
heating until the metal-coated microspheres are dry.
During the initial admixing of the raw microspheres with the
binder, heat may be applied to raise the mixture temperature up to
about 120.degree. F. to about 180.degree. F. Preferably this
temperature ranges between 140.degree. F. and 160.degree. F. As
will thus be appreciated, the present process is essentially
solvent-less.
In the aforedescribed process, the adhesive binder is first
introduced into the mixing vessel containing a quantity of
cenospheres, i.e. microspheres. Suitable techniques for applying
the binder to the microspheres include the spray or misting methods
plus direct pouring. The adhesive may thus be introduced into the
vessel in the form of a mist, liquid or vapor. During this
application, however, there should be vigorous admixing, i.e.
agitation, of the microspheres and adhesive binder to insure proper
coating of the microspheres.
Next, the desired quantity of metal flakes are added to the mixing
vessel. Preferably, the flakes are slowly added. The metal flake
addition continues until the microspheres, previously coated with
the uncured adhesive binder, are fully covered by metal flakes. The
metal flakes tend to stick to the uncured adhesive binder. An
acceptable and suitable metal flake coating is readily determined
by visual inspection. For more critical end-use applications, more
control may be required and in such cases inspection of periodic
samples, for example, under a 40 power microscope is an exemplary
control technique.
Exemplary end use applications of the products of the present
process include:
(a) use in composite materials to control static electricity in
critical applications such as in operating rooms and aircraft;
(b) use in shielding layers in microcircuitry, such as printed
circuit boards;
(c) use in molding wherein either solid or flexible substrates
require an outer layer having electrically conductive properties
for radio frequency shielding. Suitable molding techniques are
injection molded or in the powdered-in-mold-coating technique.
The hollow microspheres suitable for use in the present process
include a wide variety of commercially-graded microsphere products.
Exemplary suitable hollow microspheres, generally have average
particle sizes ranging from about 60 microns up through 180
microns. Such suitable hollow microspheres may, of course, have
individual particles having larger diameters, but generally the
average diameter falls within the above-stated range. More
particularly, the hollow microspheres have an average particle size
diameter ranging between 100 microns and 180 microns and still more
particularly from 100 to 150 microns. Most advantageously, the
microspheres have a narrow distribution of average particle sizes.
The size of the hollow microspheres employed in the present
process, from an average diameter particle size perspective, will
affect the weight percent of the metal flakes employed in the
present process. The larger hollow microspheres will require
greater quantities of metal flakes.
Advantageously, hollow fly ash microspheres are employed in the
present process to produce the present products. Such hollow
microspheres exhibit high compressive strengths and thus can
withstand considerable amounts of shear generated in intensive
mixing. An exemplary fly ash hollow microsphere suitable for use
herein is described, constituents wise, in Table I.
TABLE I ______________________________________ Chemical Analysis of
Typical Fly hollow Ash Microspheres Ingredient % By Weight
______________________________________ Silica (as SiO.sub.2)
55.0-66.0 Alumina (as Al.sub.2 O.sub.3) 25.0-30.0 Iron Oxides (as
Fe.sub.2 O.sub.2) 4.0-10.0 Calcium (as CaO) 0.2-0.6 Magnesium (as
MgO) 1.0-2.0 Alkalai (as Na.sub.2 O, K.sub.2 O) 0.5-4.0
______________________________________
The hollow microspheres are essentially dry; such core materials
are thus, preferably, substantially water-free prior to use in the
present process.
In the present process, the microspheres are admixed with about 3
to about 6 weight percent of a binder adhesive, based on the final
product. The binder adhesive may also be used in a lesser amount
ranging from about 3 to about 4 weight percent, again based on the
final product.
The adhesive binder employed in the present process is preferably a
type of adhesive. More particularly, the binder is composed of an
organofunctional silane having an organoreactive radical function
that can be polymerized at elevated temperatures along with a
reactive diluent. The diluent tends to extend the silane and also
copolymerizes with it.
The inorganic moiety of the silane molecule attaches to the
microsphere at the lower temperatures described in the admixing
step, and is covalently bonded thereto by a hydrolysis reaction.
During the binder curing step, the organic moiety of the silane
molecule copolymerizes and cross-links with the reactive diluent to
form a thermosetting polymer which binds the metal flakes to the
hollow microspheres.
An exemplary organofunctional silane product is, for example,
3[2(vinyl benzylamino)ethylamino]propyltrimethoxy silane. Exemplary
reactive copolymerizable constituents include, for example, various
lactones. An exemplary lactone is, for instance
gamma-butyrolactone.
The metal flakes employed in the present process are very small
sized. The flakes should have as low an average flake size as
feasible. The larger the average flake size, the more difficult it
is to provide a smooth finish with a paint or other coating
incorporating such hollow microspheres. Also, metal flake to
microsphere bonding is inconsistent at large flake sizes. More
particularly, the metal flake average size may range from about,
for example, 2 microns up through out 10 microns. Preferably, the
metal flakes range from about 6 microns to about 10 microns in
average size. Advantageously such latter range results in an
aesthetically pleasing product suitable for most all desired
end-use applications. Suitable metal components of the flakes
include, for example, zinc, aluminum, silver, copper, stainless
steel, platinum and gold.
Typically, the metal flakes are vigorously blended with the
microspheres coated with binder adhesive in an amount ranging from
about 15 to about 30 weight percent of the adhesive binder coated
hollow microsphere. Particularly, and more preferably, the metal
flakes are added in an amount ranging from about 17 weight percent
to about 25 weight percent. Most advantageously, the metal flakes
are added in an amount of about 18 to about 22 weight percent. This
latter weight percent provides most advantageous results when the
hollow microspheres have an average particle size average about
165-170 microns. Excessive metal flakes can be easily separated at
this stage or during subsequent work-up of the final product.
During the binder curing step, the temperature is preferably raised
and maintained at less than about 350.degree. F. and advantageously
less than 300.degree. F. More particularly, the temperature is
substantially uniformly raised within several minutes until, by
visual observation or by other means, it is apparent that the
thermosetting binder adhesive commences curing. Typically, after
the temperature has been slowly raised up to about 220.degree. F.
to about 240.degree. F., the binder will commence curing within a
matter of a few minutes. In large production runs, this step may be
thermostatically controlled in conjunction with suitable timing
mechanisms.
The heating is critical. Excessive caloric application or an
excessive rate of application thereof leads to improperly cured
products and defects. Defects result, for example, since the
coefficient of expansion for the metals exceeds that of the hollow
microsphere. Thus, excessive heat expands the metal flake and
breaks the metal flakes loose from the microsphere during, for
instance, step (c).
After the binder commences curing, the curing product is very
carefully but intermittently tumbled or admixed on a cycle basis.
The intermittent tumbling or cycling may occur off and on for
several minutes or longer. For example, in a blender, mixer, or
other similar conventional apparatus, the curing products are left
in a non-agitated state for a few minutes, admixed or tumbled for a
very brief period or time, on the order of half minutes, followed
by a non-agitated state. This intermittent cycling or
admixing/tumbling may occur about 15-20 times during this step of
the present inventive procedure. During this step various
by-products such as, for example, water of hydration or methyl
alcohol are removed. In addition, the intermittent admixing or
tumbling insures that the binder adhesive properly cures while at
the same time the metal flakes are not split off the
microspheres.
The products of the present process have excellent physical
properties and unexpectedly can replace up to about 10 times their
weight of plain metal in conventional applications. In addition,
dissipative coatings containing such products have advantageous
properties.
While the invention has been described in connection with what is
presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention is not to be
limited to the disclosed embodiments but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims, which
scope is to be accorded the broadest interpretation so as to
encompass such modifications and equivalent structures.
* * * * *